Hydrocephalic
New member
Hi all,
I have a 2007 Mercury 40hp efi 4stroke with an intermittent issue which is becoming more constant and I am hoping to find some suggestions. Quick background: I bought the boat/motor 18 months ago. It had been used infrequently by former owner. I didn't flush the fuel tank unfortunately.
It ran perfectly for probably 15 trips when suddenly it began to get stuck between 3500 and 4100 RPM at WOT. It would occasionally start running perfectly, then sometimes running as described and unable to get up on plane at WOT. It has even done this in the middle of a run where it is flying down the lake on plane and suddenly bogs down and stays at the ~4000 RPM and not on plane.
So far I've changed the fuel filter and swapped out all fuel for fresh fuel. Tested fuel pressure at the VST, it's steady at 42psi from idle through WOT and holds steady even after the boat's been off and loaded on the trailer. The primer bulb stays firm while running and all lines look new.
I've read a similar symptom from a faulty float in the equivalent of the VST that was somewhat common in the 60hp+ models, but haven't read of that being an issue with the 40hp.
Any suggestions on what this may be or what I should check next? The motor never dies, and still occasionally runs perfectly, but I cannot for the life of me figure out a common theme to the problem.
I have a 2007 Mercury 40hp efi 4stroke with an intermittent issue which is becoming more constant and I am hoping to find some suggestions. Quick background: I bought the boat/motor 18 months ago. It had been used infrequently by former owner. I didn't flush the fuel tank unfortunately.
It ran perfectly for probably 15 trips when suddenly it began to get stuck between 3500 and 4100 RPM at WOT. It would occasionally start running perfectly, then sometimes running as described and unable to get up on plane at WOT. It has even done this in the middle of a run where it is flying down the lake on plane and suddenly bogs down and stays at the ~4000 RPM and not on plane.
So far I've changed the fuel filter and swapped out all fuel for fresh fuel. Tested fuel pressure at the VST, it's steady at 42psi from idle through WOT and holds steady even after the boat's been off and loaded on the trailer. The primer bulb stays firm while running and all lines look new.
I've read a similar symptom from a faulty float in the equivalent of the VST that was somewhat common in the 60hp+ models, but haven't read of that being an issue with the 40hp.
Any suggestions on what this may be or what I should check next? The motor never dies, and still occasionally runs perfectly, but I cannot for the life of me figure out a common theme to the problem.